Project Summary: Investigating Organ Formation and the Emergence of Complexity in the Visual System Using Comparative Developmental Approaches The visual system has long been at the heart of research into the evolution of complexity in the animal kingdom. Even Darwin in On the Origin of Species addressed the evolution of the vertebrate eye as a unique and difficult case in the study of evolution. Despite a long history of research in Drosophila and vertebrate models, we still understand surprisingly little about how complex organ systems like the visual system are generated. For example, we have long known that Pax6 and other retinal determination network genes are essential to eye development in both Drosophila and vertebrates, suggesting a common origin for all visual organs. However, differences in gene regulatory network connectivity support independent evolution of parts of this canonical network. This highlights our lack of understanding of how networks change and how they relate to the complex tissues they underlie. Here we propose to leverage comparative developmental biology to better understand how gene regulatory networks, protein function, cell fate, and tissue movements evolved to generate the complexity and diversity within photoreceptive systems found across the animal kingdom. The power of comparative approaches is that they can reveal non-obvious and conserved mechanisms found common to organ formation. Recognizing these mechanisms not only deepens our basic understanding of complex organ development, it can generate new disease candidates and practical new models for human health. First, we will investigate how complex morphologies of visual organs develop by evaluating cell behavior and tissue morphogenesis during eye vesicle formation in the cephalopod Doryteuthis pealeii. Second, we will identify conserved mechanisms generating cell type diversity within the retina, specifically focused on Notch signaling in neuroepithelial tissues. Lastly, we will evaluate the core retinal determination gene regulatory network across the animal kingdom using both functional and bioinformatics tools to identify conserved network connections. This work will be the most in depth analysis to date of the relationship between gene regulatory networks to cell differentiation and tissue morphogenesis across multiple species. Our current lack of understanding of this relationship generates a barrier to translate research in model organisms to effective disease treatment efficiently and this work will shed light on better approaches to these translational steps.